Azo pigments are a class of colorants that are adequately strong tinctorially and relatively inexpensive. Azo pigments are generally either monoazo or disazo pigments. Monoazo pigments generally exhibit good lightfastness and are useful as coloring agents for paints and some printing inks. In plastics, however, some monoazo pigments tend to undesirably bloom and discolor at high temperatures, so their use is disfavored.
Commercially available azo pigments that exhibit some heat stability commonly used in plastics are limited to the color range of yellow, orange and red colors such as Pigment Yellow 61, Pigment Yellow 62, Pigment Yellow 183, Pigment Yellow 191, Pigment Yellow 205, Pigment Yellow 206, Pigment Yellow 209, Pigment Yellow 209:1, Pigment Yellow 210, Pigment Yellow 212, Pigment Orange 79, Pigment Red 60:1, Pigment Red 276, Pigment Red 277, Pigment Violet 51 and Pigment Violet 52, etc. In near masstone shades Pigment Red 276 and Pigment Red 277 are relatively warm reds with respective hue angles of 29° and 23° whereas Pigment Violet 52 is a very blue shade red with a hue angle of 9.6°. Consequently, there remains a need in the intermediate shade range for red color pigments that show desirable performance in properties such as color strength, resistance to polar solvents, light fastness and/or heat stability. It is desirable to extend the shade range of azo red pigments to intermediate red shades.